Details of how power is used are described as "audio unit and XM radio (04-06 models)". Audio unit is a box on wiring diagram w/ no internal wiring shown. It is likely the power is routed to clock and memory but no way to be certain.

1. With Fuse No. 32 removed; but, Fuse 5 installed, measure for voltage on the Yel/Red wire at the 20P light blue connector for the radio. This is to first check there is no wiring short, where the Fuse 5 Wht/Grn wiring may be accidentally touching the Fuse 32 Yel/Red wire.

2. If there is no wiring short, then you may want to open up the audio unit and examine the printed circuit board for any solder bridges, damaged components, etc.; to check for what may be causing a possible short inside the audio unit.

This link and the attached service bulletin shows how to open the audio unit and what it looks like inside.

OK, so I pulled out the radio and tested the yel/red wire for voltage with the radio removed. Didn't show any voltage at the yel/red wire with the car off and when the key turned to acc. it had voltage. Thus I'm pretty confident that it is the radio causing my problem. I put in a used radio and the problem seems to be fixed.
Is there somewhere I can send the original radio to be repaired? Thanks for all the help.

OK, so I pulled out the radio and tested the yel/red wire for voltage with the radio removed. Didn't show any voltage at the yel/red wire with the car off and when the key turned to acc. it had voltage. Thus I'm pretty confident that it is the radio causing my problem. I put in a used radio and the problem seems to be fixed.
Is there somewhere I can send the original radio to be repaired? Thanks for all the help.

I also have 2005 accord lx se with the same problem i also bought a used radio it did fine for maybe 3yrs now guess what i am having same problem again.radio plays and clock lights up w no key.honda says they have never heard of the problem but yet i called them 3yrs ago when i 1st started having the issuse the 1st time

UPDATE: OK, so I had the used replacement radio in for 2 weeks. The problem of it turning on by itself without the key is gone but it seems to turn off and back on again while driving. I checked the connections and everything is plugged in good so I think I'm going to return it for another replacement.
Before I put the original back in I thought I'd take it apart to see if I could notice anything unusual but no luck. So I put it back together and reinstalled it in the car along with a rocker switch in line on the white/green wire so I can turn it off at night and not kill the battery from the radio turning on by itself without the key in. That worked.
Now I think something went wrong from separating the radio from the bracket and putting it back together because the power button on the bracket controls is not working to turn the radio on and off. If I hit the AM/FM button the radio turns on and works but still won't turn off by the power button. I must have did something wrong attaching the radio unit to the control bracket???
Hopefully I get a good working replacement the second time around but still would like to know what's going on with my original unit?
Any thoughts will be appreciated, Thanks

I finally found the culprit causing my 2005 Accord radio to come on when the car was OFF. A surface mount resistor was NOT soldered on the ground side.
See the attached picture, The dental pic is on the resistor next to D809. I had to scrape some paint from the ground to get it to take solder. This resistor is a pull down for the on/off logic. Drove me nuts, I traced every run from the power input through several resistors. This resistor moved when I tried to solder the side opposite the ground. Radio has behaved normally ever since. Hope this helps someone, that radio is not only hard to find, it's expensive. Single CD disk player part number 39050-SDA-A020-M1. See this link: https://www.hondaaccordforum.com/for...34/#post373997